Packaging containers of the single use disposable type for liquid foods are often produced from a packaging material of the type mentioned above. Once such commonly occurring packaging container is that which is marketed under the trademark Tetra Brik® and which is principally employed for liquid foods such as milk, fruit juice etc. The packaging material in this known packaging container typically comprises a core layer of paper or paperboard and outer, liquid-tight layers of thermoplastic.
In order to render the packaging container light- and gas-tight, in particular oxygen gas-tight, as well, the material in these packaging containers is normally supplemented with at least one additional layer, often an aluminium foil (Alifoi]) which moreover renders the packaging material thermosealable by inductive thermosealing which is a rapid and efficient sealing technique for obtaining mechanically strong, liquid- and gas-tight sealing joints or scams during the production of the containers.
Packaging containers are nowadays most generally produced by means of modem packing machines of the type which form, fill and seal packages from a web or from prefabricated blanks of packaging material.
From, for example, a web, packaging containers are produced in that the web is reformed into a tube by both of the longitudinal edges of the web being united to one another in an overlap joint. The tube is filled with the intended relevant contents and is divided into individual packages by repeated transverse seals of the tube a distance from one another below the level of the contents in the tube. The packages are separated from the tube by incisions in the transverse seals and are given the desired geometric configuration, normally parallelepipedie, by fold formation along prepared crease lines in the packaging material.
From consumer quarters, it is desirable that the packaging container be easy to handle and easy to open when it is time to empty the package of its contents, and in order to satisfy this need, the packaging container is often provided with some type of opening arrangement, with the aid of which it may readily be opened without the need to employ scissors or other implements.
A commonly occurring opening arrangement in such packaging containers includes a hole punched in the core layer of the package wall, the hole being covered, on the inside and outside of the package wall, by the respective outer layers of the packaging wall which are sealed to one another in the region of the opening contour of the through-going hole. Moreover, the prior art opening arrangement generally has a separate pull-tab or opening strip which is applied over the hole and which is rupturably sealed to the outer layer of the outside of the package wall along a sealing joint around the entire opening contour of the hole and at the same time permanently sealed to the outer layer in the region inside the opening contour of the hole.
When the packaging container is to be opened and emptied of its contents, the pull-tab or opening strip is pulled off, the rupturable seal between the pull-tab and the outer layer being ruptured at the same time as the two outer layers are torn off along the opening contour of the hole and accompany adhering to the pull-tab for exposure of the through-going hole through which the contents of the packaging container may thereafter readily be poured.
One precondition for this opening arrangement to function efficiently and expediently and expose all of the pouring hole is thus that the permanent seal between the pull-tab and the outer layer on the outside of the packaging wall is sufficiently strong so as not to be ruptured when the pull-tab is pulled off, and further the seal between the two outer layers must, within the region of the opening contour of the hole, also be sufficiently strong to ensure that both of the layers are pulled off adhering to one another.
Both of these preconditions are, as a rule, easy to satisfy with packaging containers in which both of the respective outer layers of the packaging material consist exclusively of simple, easily sealed thermoplastic layers, while, on the other hand, it is not an uncommon occurrence that problems arise in packaging containers in which one or both of the outer layers of the packaging material also include a layer of another material than thermoplastic, such as, for example, an aluminum foil which is often employed in packaging containers for oxygen gas-sensitive products, such as juice, etc.
When the outer layer on the inside of the packaging wall also includes an aluminium foil which, by the intermediary of a sealing- or lamination layer, is connected to the outer layer on the inside of the packaging wall within the region of the opening contour of the hole, it occasionally happens that the seal between the two outer layers of the packaging wall is unintentionally ruptured when the opening strip or pull-tab is pulled off, and that the outer layer on the inside of the packaging wall at best is only partly removed from the hole. As a result, the remaining part of the outer layer will prevent or impede pouring out of the contents of the packaging container.